The invention relates to a method and apparatus for automatic gain control of a receiving circuit in a wireless receiver, and more particularly, to a method and apparatus for automatic gain control of a Radio Frequency Integrated Circuit (RFIC) in a Global Navigation Satellite System (GNSS) receiver.
The GNSS system is a recent system well known in the art and commonly used to determine the geodetic latitude and longitude coordinates of mobile vehicles. The current GNSS system includes Global Positioning System (GPS), Galileo, GLONASS and other satellite positioning technologies. For simplicity, a GPS receiver will be discussed herein as an example of a GNSS receiver, wherein the terms “GNSS” and “GPS” may be used interchangeably.
In general, an RFIC in a GPS receiver is designed to provide a predetermined total gain. For example, the predetermined total gain can be set to 100 dB. However, gains of some components operating at high frequency in the RFIC, such as low noise amplifier(s) and mixer(s), often change due to various factors such as process variation or circuit design, and this phenomenon will result in a poor operating point of a programmable gain amplifier, thereby degrading the performance of the RFIC.
In addition, an external low noise amplifier may be required to couple to the RFIC in the GPS receiver in order to reduce the whole noise figure of the RFIC under certain conditions. Although the actual total gain of the RFIC will be reduced after the external low noise amplifier is coupled to the RFIC, the mentioned problem of unacceptable operating points for the programmable gain amplifier and the RFIC will still exist due to unstable gain variations of the components operating at high frequency in the RFIC such as low noise amplifier(s) and mixer(s).
Therefore, an efficient and economical scheme for automatic gain control of the RFIC in the GPS receiver is required.